Residential gateways or set top boxes (STBs) that are used to configure and manage data communications networks often have external power units, where the power supply or at least one or more of its components is located in an external unit. Such external units typically comprise a plug-in adapter (or AC adapter) used to convert the alternating current (AC) electricity received from the mains to the direct current (DC) electricity used to power the adapters.
Locating this functionality in an external unit provides a number of advantages, such as: reducing heat build-up in the STB, reducing the size of the STB, and enabling the separate configuration and/or certification of the external power unit as necessary for compliance with specific power supply requirements and regulations without having to reconfigure the main unit.
However, external power supplies are somewhat problematic for HPAV network STBs. Such networks can be configured to transmit data over an existing powerline infrastructure typically found in a home or small office. Accordingly, in such networks the data is transmitted over the same medium as the power to run the STB. The external power unit must therefore be configured to provide both DC voltage to the STB and pass HPAV data on a high frequency AC signal (1.7-30 MHZ).
PCT Patent Publication 2007/016031 assigned to the common assignees of the present invention and hereby included in its entirety by reference, discloses a method for using powerline phases to synchronize the scheduling of data transmission on a powerline network. As disclosed in PCT Patent Publication 2007/016031, such powerline phases are defined according to zero cross points of AC current at a low frequency (typically 50-60 Hz). Accordingly, a powerline HPAV network STB also requires low frequency AC input from which powerline phases can be determined.
Therefore, in order to operate, an HPAV STB requires three types of electrical input: DC voltage to operate the unit itself, very low frequency (50-60 Hz) AC voltage to enable zero crossing detection on the mains outlet AC cycle, and high frequency (1.7-30 MHZ) for the HPAV/G.hn data signal.